Neutron beam therapy has been shown to be efficacious in treating certain radioresistant tumors (Catteral, 1974), presumably because of the relatively greater effect of heavily ionizing (high-LET) particles on hypoxic tumor cells. In this trial a fixed neutron dose of 1440 rads was given using a fixed beam energy of 7MeV and a constant treatment dose of 12 fractions over four weeks. This procedure may not be equally effective with different tumor types, equally well-tolerated in different sites or optimal in the sense of yielding the highest probability of uncomplicated cure in any given situation. Our objective is to explore: first, the efficacy and safety of neutron beam therapy in tumors normally unresponsive to conventional radiotherapy, determining what response rates can be obtained with specific "radioresistant" tumor types and the tolerance limits of key organ systems in which the tumors arise; and secondly, the feasibility of optimizing the treatment schedule identifying that particular combination of dose-per-fraction, number of fractions, and interval between fractions (an over-all treatment time) yielding the best prospect of cure without excessive normal tissue injury. Optimal treatment factors will be determined in four phases: (1) Radiobiologic characterization of neutron beams over the energy range 10 to 66 MeV, determining the trade-off between OER, RBE and depth-dose so as to yield the highest therapeutic ratio for a hypoxic tumor nidus at, say, 15 cm. below a relatively sensitive normal tissue; (2) Computer simulation and prediction of cellular responses in various tumor tissues and organs to neutron beams; (3) Design of treatment protocols which will offer patients the best prospect of cure with currently available data and at the same time provide new clinical data on both tumor response and normal tissue reactions with different dose-time relationships; (4) Analysis of results so as to identify trends which may lead to optimization of the treatment procedure. Updating parameters revising protocols appropriately, so as to identify statistically significant trends which may lead to optimization of treatment procedure.